Sequentially unlocking expansion slots

ABSTRACT

A lockout apparatus for a number of expansion slots in a printed circuit board includes a lockout mechanism for the expansion slots. Each lockout mechanism includes a lockout member movable between a first position in which its respective expansion slot is blocked, and a second position in which its respective expansion slot is open. Only a single expansion slot is available for use at any one time. In another embodiment, add-on card installed into expansion slots may be retained in the expansion slot when the next expansion slot is filled.

FIELD

The present invention is related generally to printed circuit boards,and more specifically to expansion slots for printed circuit boards.

BACKGROUND

Modern personal computers include an increasing number of separateinternal peripheral devices and components. Representative peripheraldevices include, but are not limited to, internal modems, sound cards,video adapters, graphics accelerators, accelerator boards, and the like.Representative components include, but are not limited to, cache chips,memory chips, and hard drives.

Typically, peripheral components in a computer system are connected to aprinted circuit board (PCB) such as a motherboard or the like through abus. For example, buses such as Peripheral Component Interconnect (PCI),Industry Standard Architecture (ISA), and Extended ISA (EISA) bus slotsare used in computer systems for connection of peripherals such as soundand video cards, modems, and the like. The boards inserted into theexpansion slots may be called expansion boards, expansion cards, cards,add-ins, add-ons, and the like.

In addition to PCI, ISA, and EISA expansion slots, other expansion slotsin PCBs may be used for adding new capabilities to the computer such asadding more memory, graphics capabilities, and support for specialdevices. In certain instances, add-on devices such as single in-linememory modules (SIMMs), dual in-line memory modules (DIMMs) and otherexpansion cards in computers having multiple expansion slots must beinstalled in a correct sequence for proper function of the device andthe computer after installation of the device.

In computer systems and expansion slots in which the correct sequence ofinstallation of add-ons is required, current industry standard practiceis to rely on the user to read an instruction set, either at theexpansion slot or in a separate manual, or to label the expansion slotsin the required order of use. Such practice is unreliable, as many usersdo not know that certain expansion add-ons must be correctly sequencedin multiple slots. Further, many users do not attempt to verify that theproper methods are being used to install add-ons. It is only after thecomputer does not function properly that many users turn to additionalguidance such as a manual or instruction set.

It would be desirable, therefore, to provide expansion slots that mustbe used in the proper order.

SUMMARY

The embodiments of the present invention overcome the problems of theprior art by providing a set of expansion slots in a computer in whichthe only available slot for placement of an add-on is the proper slot.In one embodiment, such a set of expansion slots includes a mechanicallockout mechanism with a cascading set of components that allows accessto only the appropriate slot at any given time. Once the currentappropriate expansion slot is filled, the next available correctexpansion slot becomes available.

In another embodiment, a lockout apparatus for a plurality of expansionslots including a first and last slot, and intermediate slots, includesa number of lockout mechanisms, one for each of the intermediateexpansion slots and the last expansion slot. Each lockout mechanism hasa lockout member movable between a first position in which itsrespective expansion slot is blocked, and a second position in which itsrespective expansion slot is open. Each of the lockout mechanismsincludes a lockout disk rotatable about a central point, the lockoutdisk having a lockout member fixedly rigidly attached to the lockoutdisk, the lockout member extending into its respective expansion slot, alockout opening aligned with the lockout channel when the lockout memberis in its first position, and a lockout rod rotatably mounted to thelockout disk. The lockout rod extends into the lockout channel andlockout opening of the adjacent expansion slot when the lockout memberis in its first position, and movable out of the lockout opening of theadjacent expansion slot when the lockout member moves to its secondposition.

In yet another embodiment, each of the lockout mechanisms includes abody having a first end and a second end, a displacement tab extendingfrom the first end, and an add-on card opening positioned between thefirst end and the second end.

In still yet another embodiment, each of the lockout mechanisms includesa power supply, a switch with a contact disposed in a first expansionslot, and a lockout solenoid in a second expansion slot, the switchconnected between the power supply and the lockout solenoid, whereinactuation of the switch actuates the lockout solenoid to retract alockout member from the second expansion slot.

A method embodiment of the present invention includes blocking access toall but the first of the plurality of expansion slots, and openingaccess to the next of the plurality of expansion slots upon installationof an add-on card into the first of the expansion slots.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of an embodiment of the presentinvention;

FIG. 2 is a side elevation view of the embodiment of FIG. 1 with anexpansion add-on in place;

FIG. 3 is a perspective view of another embodiment of the presentinvention;

FIG. 4 is a top view of an embodiment of a lockout mechanism of FIG. 3;

FIG. 5 is a view of the lockout mechanism embodiment of FIG. 4 takenalong lines 5—5 thereof;

FIG. 6 is a perspective view of the lockout mechanism embodiment of FIG.4;

FIG. 7 is a perspective view of the embodiment of FIG. 3 with anexpansion add-on in place;

FIG. 8 is a side elevation view of yet another embodiment of the presentinvention;

FIG. 8A is a side elevation view of still another embodiment of thepresent invention;

FIG. 9 is a side elevation view of another embodiment of the presentinvention;

FIG. 9A is a side elevation view of the embodiment of FIG. 9 with anexpansion add-on in place;

FIG. 9B is a side elevation view of the embodiment of FIG. 9 with asecond expansion add-on in place;

FIG. 10 is a schematic block diagram of the embodiment of FIG. 9;

FIG. 11 is a side elevation view of another embodiment of the presentinvention;

FIG. 12 is a side elevation view of yet another embodiment of thepresent invention;

FIG. 13 is a flow chart diagram of a method embodiment of the presentinvention;

FIG. 14 is a perspective view of a desktop computer on which embodimentsof the present invention may be utilized; and

FIG. 15 is a perspective view of a portable computer on whichembodiments of the present invention may be utilized.

DESCRIPTION OF EMBODIMENTS

In the following detailed description of the embodiments, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

FIG. 1 shows a view of one embodiment 100 of a lockout mechanism forexpansion slots. Lockout mechanism 100 comprises in one embodiment fourexpansion slots 102, 104, 106, and 108, each expansion slot having anadd-on opening 110, 112, 114, and 116, respectively, capable ofaccommodating an add-on such as a memory chip or the like. Eachexpansion slot 102, 104, 106, and 108 also has a lockout mechanism 118,120, 122, and 124, respectively. Initially, with all of the expansionslots 102, 104, 106, and 108 empty, only expansion slot 102 is capableof receiving an add-on or expansion card. Lockout mechanism 118 ismovable, by the insertion of an add-on or expansion card into expansionor add-on slot 102, between a first, available position in which anexpansion card or add-on may be inserted into expansion slot 102 to asecond, locked position in which an expansion card is positioned inexpansion slot 102.

The lockout mechanisms 118, 120, 122, and 124 are cascading lockoutmechanisms. Lockout mechanism 118 of expansion slot 102 comprises alockout disk 126 having a lock opening 128, a lockout member 130, and alockout rod or bar 132. Lockout member 130 is fixedly, rigidly attachedto lockout disk 126 at point 134, and extends tangentially from lockoutdisk 126 into expansion slot 102. Lockout rod 132 is rotatably attachedto lockout disk 126 at point 136. The lockout disk 126 is held in anangular position as shown in FIG. 1 by biasing means 138. As shown inFIG. 1, biasing means 138 is a spiral spring connected to the lockoutmember 130 at point 134 and to the expansion slot 102 at point 140.Expansion slot 102 is shown also with optional lockout rod opening 139.

Lockout rod 132 extends from expansion slot 102 into expansion slot 104.Expansion slot 104 has a lockout channel 142 into which lockout rod 132extends when the lockout mechanism 118 is in its first, availableposition. Lockout mechanism 120 of expansion slot 104 comprises alockout disk 144 having a lock opening 146, a lockout member 148, and alockout rod 150. Lockout member 148 is fixedly, rigidly attached tolockout disk 144 at point 152, and extends tangentially from lockoutdisk 144 into expansion slot 104. Lockout rod 150 is rotatably attachedto lockout disk 144 at point 154. The lockout disk 144 is held in anangular position as shown in FIG. 1 by biasing means 156. As shown inFIG. 1, biasing means 156 is a spiral spring connected to the lockoutmember 148 at point 152 and to the expansion slot 104 at point 158.

Expansion slot 108, the last expansion slot shown in FIG. 1, has no needfor a lockout rod such as rods 132 and 150, unless slot 108 is not thelast expansion slot in the apparatus. Similarly, the first expansionslot 102 does not need to have lock opening 128 or lockout channel 139,as they are unused. The remaining details of expansion slots 106 and 108are substantially identical to expansion slots 102 and 104, and forpurposes of brevity will not be described further herein.

Referring now also to FIG. 2, expansion slot 102 is shown with an add-oncard 200 installed therein. With the installation of add-on card 200,lockout disk 126 rotates in a clockwise direction as indicated by arrow202, and fixedly attached lockout member 130 is displaced by add-on card200. The angular movement of lockout disk 126 moves end 160 of lockoutrod 132 out of lock opening 146. When this happens, lockout disk 144,previously prevented from rotating by the engagement of lockout rod 132and lock opening 146, is free to rotate as indicated by arrow 204, andan add-on card is freely installable into expansion slot 104. Lockoutrod 150 is still engaged with lock opening 162 of lockout disk 164 oflockout mechanism 122 in expansion slot 106, preventing the insertion orinstallation of an add-on card such as card 204 into expansion slot 106.Expansion slot 108 is similarly disabled.

In another embodiment of a lockout mechanism shown in FIG. 3, lockoutmechanism 300 comprises expansion slots 302, 304, 306, and 308, eachexpansion slot having a respective add-on opening 310, 312, 314, and316. A lockout mechanism 318 is positioned over expansion slot 302 andexpansion slot 304. Lockout mechanism 320 is positioned over expansionslot 304 and expansion slot 306. Lockout mechanism 322 is positionedover expansion slot 306 and expansion slot 308. Expansion slot 302 isavailable for installation of an expansion or add-on card. However, eachof the remaining expansion slots, 303, 306, and 308, are covered by asection of lockout mechanism 318, 320, and 322, respectively.

The structure of a lockout mechanism embodiment, such as lockoutmechanisms 318, 320, and 322, is shown in detail in FIGS. 4, 5, and 6.Since each lockout mechanism 318, 320, and 322 is substantiallyidentical, only one (318) will be described in detail. Lockout mechanism318 comprises a body 400 having a first end 402 and a second end 404.First end 402 has a displacement tab 406. An add-on card opening 408 ispositioned in the body 400 between the ends 402 and 404. Between theadd-on card opening 408 and end 404 is a lockout member 412 formed frompart of the body 400. In one embodiment, displacement tab 406 is angledwith respect to the plane containing surface 410 of body 400.

When in place on a PCB or the like having expansion slots such as slots302, 304, 306, and 308, a lockout mechanism such as lockout mechanism318, 320, or 322 is positioned so as to be movable from a first positionin which displacement tab 406 is positioned over an add-on opening of afirst expansion slot and lockout member 412 is positioned over an add-onopening of a second expansion slot adjacent the first expansion slot,and a second position in which card opening 408 is positioned above theadd-on opening of the second expansion slot adjacent the first expansionslot.

As shown in FIG. 3, displacement tab 406 of lockout mechanism 318 ispositioned over expansion slot 302, and lockout member 412 is positionedover expansion slot 304. In this position, an expansion or add-on cardor chip could be installed into the first expansion slot 302, but not inexpansion slot 304 due to its being blocked by lockout member 412 oflockout mechanism 318. Similarly, lockout members 412 of lockoutmechanisms 320 and 322 block the installation of an add-on card intoexpansion slot 306 and expansion slot 308, respectively.

In FIG. 7, an add-on card 700 is shown installed into expansion slot302. In installation of add-on card 700, lockout member 318 is displacedfrom its first position as shown in FIG. 3 to its second position. Ininstallation of add-on card 700, add-on card 700 contacts displacementtab 406 of lockout mechanism 318, and during the installation of add-oncard 700, displaces lockout mechanism 318 in the direction of arrow 702.When lockout mechanism 318 is displaced as shown, lockout member 412 oflockout mechanism 318 is removed from its position over the expansionslot 304. In this movement of lockout mechanism 318, card opening 408 ismoved into position over expansion slot 304. This in turn exposesdisplacement tab 406 of lockout mechanism 320. In this position, asecond add-on card 701 can be freely installed in expansion slot 304.

Since neither lockout mechanism 320 nor lockout mechanism 322 has beenmoved from its initial position, add-on slots 314 and 316 of expansionslots 306 and 308 are blocked from installation of an add-on card bylockout members 412 of lockout mechanisms 320 and 322, respectively.

In another embodiment 800, shown in side elevation in FIG. 8, expansionslots 802, 804, 806, and 808 are used with lockout mechanisms 810, 812,and 814. Lockout mechanisms 810, 812, and 814 are biased in thedirection indicated by arrow 816 by biasing means 818, 820, and 822respectively. When an add-on card such as add-on card 824 is installedinto an expansion or add-on slot such as expansion slot 802, the card824 pushes the lockout mechanism 810 as has been described above.Biasing means 818, in one embodiment a spiral spring, biases the lockoutmember 810 in the direction of arrow 816. In one embodiment, add-on card824 has a notch 826 which the displacement tab 828 of lockout member 810engages upon installation of the add-on card 824 into expansion slot802. A force on the lockout member 810 in the direction of arrow 830 ora force on the add-on card 824 in the direction of the arrow 832, orsome combination thereof, will then be required to remove add-on card824 from expansion slot 802. The force on the lockout member may beasserted by use of a release tab 834 located on the lockout member 810.

In FIG. 8A, another embodiment of a means for retaining an add-on cardin its expansion slot when an add-on card is installed into the nextexpansion slot is shown. For purposes of clarity, no further detail isshown. The embodiment 850 works equally well with the lockout apparatusembodiments 100, 300, and 900. In this embodiment 850, expansion slots852, 854, 856, and 858 have therebetween retention members 860, 862, and864. Retention member 860 extends between expansion slots 852 and 854,retention member 882 extends between expansion slots 854 and 856, andretention member 864 extends between expansion slots 856 and 858.

Each retention member 860, 862, and 864 is substantially identical tothe others. Therefore, only retention member 860 will be described indetail. Retention member 860 is positioned so that its end 866 extendsinto expansion slot 854 when no add-on card is installed in expansionslot 854. When an add-on card 872 is installed in expansion slot 852,expansion slot 854 becomes available for installation of add-on card874. When add-on card 874 is installed into expansion slot 854, theadd-on card 874 contacts and displaces retention member 860 so that end868 of retention member extends into slot or recess 870 of add-on card872, retaining card 872 in expansion slot 852 until add-on card 874 isremoved from expansion slot 856.

In yet another embodiment shown in FIG. 9, an electronic lockoutapparatus 900 for PCB expansion slots comprises a PCB 902 having aplurality of expansion slots 904, 906, 908, and 910. Expansion slots906, 908, and 910 each have a lockout mechanism 924, 926, and 928respectively. In one embodiment, each lockout mechanism comprises asolenoid which moves a lockout member between a first position in whichthe lockout member blocks access to an expansion slot and a secondposition in which the lockout member is removed from blocking access tothe expansion slot.

In FIG. 9, lockout mechanism solenoids 924, 926, and 928 each have alockout member 930, 932, and 934 respectively. Each lockout member iscapable of blocking or of allowing access to expansion slots 904, 906,and 908, respectively. Expansion slots 904, 906, 908, and 910 each havetherein a switch 912, 914, 916, and 917, each switch having first andsecond terminals, each switch having its first terminal connected to apower supply (not shown). Each switch extends into its respectiveexpansion slot. The second terminal of each switch is connected to oneor more solenoids as follows. Switch 912 is operatively connected tolockout solenoid 924 of expansion slot 906. Switch 914 is operativelyconnected to retention solenoid 918 of expansion slot 904 and to lockoutsolenoid 926 of expansion slot 908. Switch 916 is operatively connectedto retention solenoid 920 of expansion slot 906 and to lockout solenoid928 of expansion slot 910. Switch 917 is operatively connected toretention solenoid 922 of expansion slot 908.

In initial operation of the embodiment 900, lockout members 930, 932,and 934 are in their first position, each lockout member blocking accessto its respective expansion slot. While connection to a retentionsolenoid is shown, it should be understood that sequential access toexpansion slots does not depend on physical retention of an add-on cardin the expansion slot.

Referring now also to FIG. 9A, when an add-on card such as add-on card936 is to be installed into the embodiment 900, the only availableexpansion slot is expansion slot 904. The remaining expansion slots,906, 908, and 910, are blocked from access by lockout members 930, 932,and 934 respectively. When add-on card 936 is installed into expansionslot 904, it actuates switch 912 to complete an electric circuit betweenthe power supply and lockout solenoid 924, actuating lockout solenoid924, causing lockout member 930 to be retracted, allowing free access toexpansion slot 906 for a next add-on card to be installed therein. Theremaining lockout members 932 and 934 remain in their first positionsblocking access to expansion slots 908 and 910 respectively. Add-on card936, the last add-on card installed into the expansion slots of PCB 902,is freely removable from expansion slot 904 at this point.

In another embodiment shown in FIG. 9B, upon the installation of asecond expansion or add-on card into expansion slot 906, switch 914 isactuated. This in turn actuates lockout solenoid 926 to retract lockoutmember 932, and actuates retention solenoid 918. When actuated,retention solenoid 918 extends retention member 938. A mating opening orrecess 940 in add-on card 936 is engaged by retention member 938,retaining add-on card 936 in expansion slot 904. In this embodiment whenall expansion slots 904, 906, 908, and 910 are full, only the add-oncard in expansion slot 910 is capable of being removed.

Removal of the add-on card in expansion slot 910 will de-actuate switch917, and retention solenoid 922 will retract its retention member. Inthis state, an add-on card may be installed into expansion slot 910,which will re-actuate switch 917 and retention solenoid 922, or theadd-on card in expansion slot 908 may be freely removed. This willde-actuate switch 916, causing the extension of lockout member 934 oflockout solenoid 928 and the retraction of the retention member ofretention solenoid 920.

In another embodiment, instead of sequential access to expansion slots,the solenoids and switches described above may be operatively connectedin any pattern of expansion slot access. For example, operativelyconnecting switch 912 with lockout solenoid 926, switch 916 with lockoutsolenoid 924, and switch 914 with lockout solenoid 928 will cause theexpansion slots to become available, in order, 904, 908, 906, and 910.Any variation of expansion slot availability order is therefore capable,and is within the scope of the invention. Of course, expansion slot 904may be equipped with an appropriately connected lockout solenoid, andexpansion slot 910 may be equipped with an appropriately connectedswitch and retention solenoid for operation of the expansion slotavailability in any chosen order. Further, more or fewer expansion slotsmay be connected without departing from the scope of the invention.

All solenoid discussed herein are in one embodiment flip flop solenoids.A flip flop solenoid requires only momentary energization to move itsmovable member, in one embodiment a lockout member or a retentionmember, from its first position to its second position, or from itssecond position to its first position. When using flip flop solenoids,power consumption of the embodiment is reduced, as is wear and tear onphysical components of the solenoids.

FIG. 10 is a schematic diagram of the embodiment 900 shown in FIG. 9.Power supply 1000 is connected to switches 912, 914, and 916. Whenswitch 912 is actuated, solenoids 918 and 924 are actuated. When switch914 is actuated, solenoids 920 and 926 are actuated. When switch 916 isactuated, solenoids 922 and 928 are actuated.

In another embodiment 1100, shown in side elevation in FIG. 11,expansion slots 1102, 1104, 1106, and 1108 are used with lockoutmechanisms 1110, 1112, and 1114. Each of the lockout mechanismscomprises a cover arm (1116, 1118, and 1120) and a lockout member (1122,1124, and 1126), and each lockout mechanism is rotatable about a pivotpoint (1128, 1130, and 1132) between a first rest position and a secondoperational position. Lockout members 1122, 1124, and 1126 may be rods,wires, or other members which block access to an expansion slot withoutdeparting from the scope of the invention. Lockout mechanism 1110 isshown in operational position with an expansion card or add-on 1134 inplace in expansion slot 1102. Lockout mechanisms 1112 and 1114 are shownin their rest positions. When expansion card or add-on 1134 ispositioned in expansion slot 1102, the card 1134 pushes down on coverarm 1116. The lockout mechanism 1110 rotates about pivot point 1128,moving lockout member 1122 out of the way of expansion slot 1104,allowing another expansion card or add-on to be inserted into expansionslot 1104.

Lockout mechanisms 1112 and 1114 are shown in lockout positions in whichthe expansion slots 1106 and 1108 will not accept an expansion card oradd-on. In the position shown, expansion alot 1104 will accept anexpansion card or add-on since the lockout member 1122 of lockoutmechanism 1110 has been removed from blocking the expansion slot 1104 byinsertion of the expansion card or add-on 1134 into expansion slot 1102.

In one embodiment, when an expansion card or add-on such as add-on 1134is removed from an expansion slot, gravity causes the lockout mechanismto rotate about its pivot point, and the lockout mechanism returns toits rest position. This rest position is shown for lockout mechanisms1112 and 1114 in FIG. 11. In another embodiment, the lockout mechanismsmay be biased toward the rest position, so that when an expansion cardor add-on is removed from an expansion slot, the lockout mechanism isurged into its rest position.

In another embodiment 1200, shown in side elevation in FIG. 12,expansion slots 1202, 1204, 1206, and 1208 are used with lockoutmechanisms 1210, 1212, and 1214. Each of the lockout mechanismscomprises a cover arm (1216, 1218, and 1220), a lockout member (1222,1224, and 1226), and a gear (1228, 1230, and 1232). Each lockoutmechanism is rotatable about a pivot point (1234, 1236, and 1238)between a first rest position and a second operational position. Teethon each gear engage notches or detents in the lockout member. Lockoutmechanism 1210 is shown in operational position with an expansion cardor add-on 1240 in place in expansion slot 1202. Lockout mechanisms 1212and 1214 are each shown in their rest position. When expansion card oradd-on 1240 is positioned in expansion slot 1202, the card 1240 pushesdown on cover arm 1216. The lockout mechanism 1210 rotates about pivotpoint 1234, moving lockout member 1222 out of the way of expansion slot1204 through the engagement of the teeth of gear 1228 and the notches ordetents of lockout member 1222. Another expansion card or add-on maythen be insterted into expansion slot 1204.

Lockout mechanisms 1212 and 1214 are shown in rest or lockout positionsin which the expansion slots 1206 and 1208 will not accept an expansioncard or add-on. In the position shown, expansion slot 1204 will acceptan expansion card or add-on since the lockout member 1222 of lockoutmechanism 1210 has been removed from blocking the expansion slot 1204 byinsertion of the expansion card or add-on 1240 into expansion slot 1202.

In one embodiment, the gears 1234, 1236, and 1238 are biased in thedirection of arrow 1242, so that when an expansion card or add-on isremoved from an expansion slot, the lockout mechanism returns to itsrest position. The lockout mechanism may be biased in many ways,including by way of example but not limitation, springs including coil,leaf, and spiral springs, gear tension, and the like.

In another embodiment, each of the embodiments discussed above isimplemented with a series of light emitting diodes (LEDs) to indicatedwhich of the add-on slots is available for installation of an add-oncard. Such a series of LEDs could be actuated by mechanical switchesclosing to light an LED when the add-on slot is available forinstallation of an add-on card. Also, LEDs could be used to indicatewhether an expansion slot is full, available, locked, or any combinationthereof.

A method embodiment of the present invention is shown in flow chartdiagram in FIG. 15. Embodiment 1500 comprises blocking access to allexpansion slots but the first expansion slot of a set of expansion slotsin block 1502, and allowing access to the next expansion slot in the setof expansion slots upon installation of an add-on card in the firstexpansion slot in block 1504. Optionally, the first add-on card may beretained in the first expansion slot upon installation of an add-on cardin the second expansion slot in block 1506, and the first add-on cardmay be made removable from the first expansion slot upon removal of thesecond add-on card in block 1508.

It may be seen that more complicated lockout mechanisms with differentcard opening positions or even multiple card openings, as well asdifferent orientations of the various lockout mechanisms, could allow aPCB to employ a scheme in which the expansion slot opening use waschosen in any order. For example, if the expansion slot add-on order isnot sequential, the placement, orientation, and configuration of lockoutmechanisms could be chosen to allow any order of use for the expansionslots without departing from the scope of the invention.

It should be understood that although four expansion slots are shown inthe various embodiments, fewer or more expansion slots may be usedwithout departing from the scope of the invention. It should also beunderstood that the physical location of expansion receptacles or slotson a PCB are chosen to accommodate the functionality of the lockoutmechanism embodiment.

Desktop computers, as shown in FIG. 14, typically include a monitor1400, keyboard input 1402, central processing unit 1404, and a pointingor selection device such as mouse 1405. Further components of a typicalcomputer system may include a machine readable storage media such asdisk drive 1406, hard disk, CD-ROM 1408, DVD, modem, and the like. Theprocessor unit of such a computer typically includes a microprocessor,memory (RAM and ROM), and other peripheral circuitry, not shown.Portable or laptop computers, as shown in FIG. 15 include the samefeatures in general as desktop computers, but are smaller, and oftencomprise a single unit 1500 with integrated display screen 1502 andkeyboard 1504, and pointing device 1505 such as a touch pad ortrackball. Such computers are some of the types of host devices on whichembodiments of the present invention may be employed.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A method of sequential access to a plurality ofexpansion slots of a printed circuit board, the method comprising:blocking access to all but the first of the plurality of expansionslots; and automatically opening access to the next of the plurality ofexpansion slots upon installation of an add-on card into the first ofthe expansion slots.
 2. The method of claim 1, and further comprising:retaining the first add-on card in the first expansion slot uponinstallation of a second add-on card in the second expansion slot. 3.The method of claim 2, and further comprising: allowing removal of thefirst add-on card upon removal of the second add-on card.
 4. The methodof claim 1, wherein the expansion slots are accessed sequentially. 5.The method of claim 1, wherein the expansion slots are accessed in apredetermined order.